1. Field of the Invention
The present invention relates to a sampled video processors, and in particular, to video sample rate converters.
2. Description of the Related Art
Digital video effects systems, including digital video effect generators and video combiners, are well known and widely used in the art. Generally, a digital video effects system receives at least two video input signals, with one selected for use as a video fill signal and the other selected for use as a video background signal. This selection involves another input signal, i.e. a key signal, which selectively keys the fill video over the background video. If the video input signals are digital, they are typically in accordance with the SMPTE D1 standard. However, sometimes one or more of the input signals may be in accordance with the SMPTE D2 standard, thereby requiring conversion to the SMPTE D1 standard. These video signals can then be processed in accordance with a number of well known video effects. For example, the fill video can be keyed onto the background video with perspective or rotational effects, or a video image can be constructed which appears to be a three-dimensional object with fill video occupying the faces of the object. While all of the foregoing, and much more, can be achieved with conventional digital video effects systems, many limitations have existed.
A problem with conventional systems involves video sampling rates. Frequently, an available video signal is a composite video baseband signal sampled at a frequency of approximately 14.3 MHz, according to the SMPTE D2 standard. However, systems must often be operated according to the SMPTE D1 (CCIR 601) standard, requiring a component video baseband signal sampled at a frequency of approximately 13.5 MHz. Conventional video sample rate converters have used a plurality of multi-tap finite impulse response ("FIR") digital filters (e.g. one each for both the luminance and chrominance component signals) with time variant filter coefficients to provide this rate conversion. However, such rate converters involve complex circuits requiring many components and a relatively large amount of space.